Induction electric furnace



S p 1931- E. F. NORTHRUP I 1,822,539

INDUCTION ELECTRIC FURNACE Original Filed March 9. 1929 I {Z J6 I w 10 COMMERCIAL rxequzucv.

INV "TOR Patented Sept. 8, 1931 UNITED STATES PATENT OFFICE.

EDWIN FITCH NORTHRUP, OF PRINCETON, NEW JERSEY, ASSIGNOR TO AJAX ELEC- TROTHEBMIC CORPORATION, OF AJAX PARK, NEW JERSEY, A CORPORATION OF NEW JERSEY INDUCTION ELECTRIC FURNACE Application filed March 9, 1929, Serial No. 845,664. Renewed February 4, 1931.

My invention relates to induction heating furnaces to which currents of two-frequencies are to be applied.

The main purpose of my invention is to I provide for either independent heating or stirring of the furnace pool or for concurrent heating and stirring of the content of the pool by separate coils.

A' further purpose is to use separate pool surrounding furnace coils for the purpose of heating from one source of supply with little stirring or stirring-from a second source of supply with little heating or concurrently applying both sources of supply to most e 18 cientl heat and stir.

A filrther purpose is to provide for intermittent or alternative application of electric current of different frequencies to the same furnace pool and permissibly through the 50 same coil, using a current of commercial, or at least of relative low frequency for stirring the molten bath and a difl'erent current of very much higher frequency for melting or for heating molten metal.

A further purpose is to permit the use of the same coil for induction at different frequencies by merel connecting sources of supply of widely different frequencies to the coil at will and thus heating and stirring to any total extent and in any proportion which may be desired.

Further urposes will appear in the specification an in the claims.-

My invention relates to the methods involved as well as to apparatus by which the methods may be carried out.

I have preferred to illustrate one general invention only in several slightly dlflerent embodiments.

Figures 1, 2 and 3 are diagrammatic views showing slightly difi'erent variations of the same invention.

In the drawings similar numerals indicate like parts. a

This application is a continuation for certain purposes of my application for Inductor type furnace, Serial No. 312,774, filed October 16, 1928.

My invention is directed to the use of alternating electric current of two widely different frequencies in a pool-surrounding furnace lnductor or inductors to the best advantage for the two functions of heatin and stirring a molten bath, either separate y or together.

In such a furnace the heating effect of the current varies with the frequency as well as wlth the square of the ampere turns, whereas the stirring effect is substantially independent of the frequency but varies with the square of the ampere turns. For equal power 1n ut a high requenc furnace, because of t e vary rapid rate 0 change of the high frequency current, will have a very much lower current than the current in a furnace of much lower frequency For this reason for equal power input the stirrin effect of the much smaller current in the igh frequency furnace will be very much less than the stirring eifect of the much larger current in the lower frequency furnace. This is obviously because the square of the ampere turns of the hi her frequency small current will be very muc less than the square of the ampere turns of the lower frequency circuit having large current.

My invention takes advantage of this condition to use a large current of commercial or relatively low frequenc for the stirring effect and to use a high requency current for the heating effect.

In metallurgical operations it is desirable to be able not only to melt, and subsequently to heat preliminarily melted metal, but to be able to stir the metal to insure thorough-mixing of the content of the molten pool with or without added treating materials. Though it may be best to perform these operations concurrently a large part of the advantage can be secured in all cases and the entire advantage in somecases by intermittently heating and stirring, applying the heating current for any predetermined length of time to secure a temperature high enough for an intended metallurgical operation,

stirring while the mixing is needed and interruptin the stirring operation if necessary to additionally heat the metal where the operation extends over too long a time. My invention is intended to take care of all of these situations by providing intermittent and concurrent highly eflicient heating with some stirring and highly efficient stirring with some heating.

In view of the situation above I have shown circuits intended for either concurrent or successive highly efiicient heating and highly efficient stirring in Figures 1 and 2 and for successive but not concurrent heating and stirring in Fi ure 3.

In Figure 1 the Furnace charge is surrounded by two sets of windings intended to be supplied with currents of different frequencies.

Of the two sources the high frequency source of supply is shown at 6 and supplies a winding shown in Figure 1 as comprising spaced coils 7 and 8 illustrated as surrounding the upper part and the lower part of the space for the furnace charge. These combine to form in efiect a single inductor. This high frequency supply is corrected for power factor by a condenser shown at 9 by which the circuit including the furnace coils is tuned or approximately tuned. This circuit is more efficient for its heating effect than for its stirring effect and is intended as the heating circuit.

The molten furnace charge within a container, diagrammatically shown at 11 is melted or additionally heated primarily by this high frequency current. When it is desired to stir the molten metal comprising the charge this is accomplished chiefly through a separate inductor coil 12 which is illustrated as supplied with a lower frequency current through a secondary 13 of a transformer 14 whose primary 16 is coupled with a preferably commerclal frequency generator 15.

The form shown in Figure 2 differs from that shown in Figure 1 in the location of the inductor coil, in that the lower frequency coil 12 surrounds a single high fre uency inductor coil which takes the place of t e two separated coils of Figure 1. With either construction the heating or stirring can be effected separately or concurrently as desired. The constructions shown are simple and inexpensive and are highly effective for the purpose intended.

In the form shown in Figure 3 the same coil 12 is used for both high frequency heating and lower frequency stirring. The high frequency supply 6 may be connected through switch 17 to the coil 12 at any two of the taps 18 so as to correspondingly vary the voltage upon condenser 9 and to vary the heating input to the furnace. The lower frequency source 15 is preferably a commercial frequency and in any event a markedly different frequency from that of the high frequency source.

The operation of this form of the furnace may correspond in all particulars with that of the furnaces shown in Figures 1 and 2 except that the two-frequencies cannot be applied concurrently. As in Figures 1 and 2 the heating (high frequency) current can be applied indefinitely until the molten metal has been brought to the desired temperature for treatment, after which the lower frequency current can be applied during the entire time of treatment, if this be not too long, or at intervals between heating applications, maintaining the temperature while effecting the desired stirring. If the stirring current be interrupted but a short time the stirring action within the molten metal will continue during the interruptions.

It will be evident that I am able to apply the heating and stirring currents within the same belts or within different belts of depth of the furnace pool, concurrently or intermittently as preferred.

It will be evident that my invention is applicable as a method or apparatus or tool in a great variety of metallurgical operations in which it is desired to use the currents at their highest efficiencies or in which it is advisable to separate the heating and stirring.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless .and scope of my invention.

Having thus described my invention, what I desire to secure by Letters Patent is 1. A multiple frequency induction furnace comprising a furnace inductor coil free from interthreaded magnetic circuit, separate sources of current therefor having widely different frequencies and switch means for connection of either of the frequencies of current to the coil at will. e

2. The method of heating and stirring molten metal, which consists in intermittently applying a high frequency current and a current of a very much lower frequency to the same pool and through the same path of current flow.

3. The method of heating and stirring a to a temperature above that required for any operation to be performedbefore applying the stirring current for mixing the charge.

4. The method of heating and stirring a pool of molten metal which consists in circulating about it successively currents of high frequency to secure the heating efiect thereof and currents of very, much lower frequency to secure the stirring efiect thereof, varying the length of time of application of each and the number of applications of each according to the comparative heating and stirring needs of the pool.

EDWIN FITCH NORTHRUP. 

